An electrostatic painting device typically uses a rotary atomizer to atomize paint or coating material. A rotary atomizer typically includes a bell shaped body (xe2x80x9cbell cupxe2x80x9d), which is typically used, but not exclusively, in painting motor vehicles. The bell cup is mounted to one end of a rotatably mounted shaft, which is typically driven by an air motor. The bell cup is generally spun at a relatively high speed, to about 70,000 RPM, to generate sufficient centrifugal force to atomize the coating material exiting the bell cup""s spray edge into a super fine mist.
Different bell cups may have different shapes and configuration to offer a variety of flow shapes and rates. Air can be supplied through a shroud that is concentrically positioned over the bell cup, adjacent to where the atomized coating material leaves the bell cup, to direct the atomized coating material to the object to be coated.
The bell shaped body can have a cavity defining an inner flow surface that communicates with the coating material source and a spray edge contiguous with the inner flow surface at the front or distal end of the bell shaped body. The bell cup is typically rotated around a stationary nozzle having a passageway or channel for the coating material.
One known problem with a bell cup atomizer is that coating material can accumulate on the outer exposed surfaces of the bell cup. During use, the accumulated (old) coating material can dislodge from the bell cup and undesirably mix with the new coating material, especially after changing the paint. Therefore, it is highly desirable to clean the outer surfaces of unwanted material.
One solution is to separately feed solvent or jet air to the outer peripheral surfaces to remove or prevent the unwanted material from adhering thereto. See for example, U.S. Pat. Nos. 5,862,988, 5,707,009, and 5,106,025. Another solution, as disclosed for example, in U.S. Pat. No. 5,707,009, uses a stationary nozzle having a plurality of channels that are separate from the coating material channel for delivering solvent to the inner flow surface and the outer surface of the bell cup. Since the solvent channels are independent from the coating material channel, the bell cup can be rinsed with solvent (rinsing or cleaning agent) without having to remove the paint from the paint channel. The feed nozzle, which is coaxially arranged with the bell cup, delivers solvent or coating material from the rear or proximal end of the bell cup through passages formed in the flow control device, e.g., an insert or face cover, of the bell cup.
In U.S. Pat. No. 5,707,009, the bell cup has an annular cavity located at the rear section of the bell cup, communicating with the solvent channels. The annular cavity creates a reservoir by which solvent flows via the rearward edge onto the outer periphery of the bell cup. During use, while the bell cup undergoes painting operation, the annular cavity is prone to paint accumulation. Thus, there is a need for a better way of cleaning the outer periphery of the bell cup. The present invention addresses this need.
Known bell-cup atomizers are typically monolithically formed (single-piece construction), typically machined from a single block of aluminum. In this vein, a typical bell cup atomizer has a bell cup integrally formed with a flow control device typically comprising a front cover or bell cone covering a portion of the cavity. The front cover or bell cone has a front side having exit passageways. The backside or the proximal end of the bell-cup atomizer has a rather relatively small passage through which the machining or cleaning is accomplished.
In practice, the atomized coating material can adhere to the surfaces of the bell cup and impede the flow of the coating material through the exit holes. Consequently, the bell cup must be cleaned frequently. Thorough cleaning of known bell cups entails detaching them from their manifold to access the internal surfaces. Even after detaching it, the narrower or smaller opening at the proximal end of the bell cup makes cleaning difficult.
Further, various stages of a coating operation may require different flow configurations of coating materials and, thus, require a different exit hole arrangement. With known bell cups, the entire bell-cup atomizer must be detached from the manifold, and an entire new bell-cup atomizer must be attached. This procedure must be repeated each time the coating operation calls for a change in the flow configuration of the coating material.
Accordingly, there is a need for a better way of accessing the internal surfaces of the bell-cup atomizer and a more economical way of manufacturing and using the same. In this respect, U.S. Pat. No. 5,707,009 addresses this problem with a detachable flow control device (insert) comprising a front cover and a ring unit. The present invention also addresses this need.
Further, a bell-cup atomizer with the integral flow control device or the detachable insert typically has radially or outwardly extending channels through which the paint exits. The bell-cup atomizer or the detachable insert can be formed with a curved or flat wall surface. The present inventor has found that paint can build up on that wall surface even after undergoing a wash cycle. Accordingly, there is a need for a bell-cup atomizer or detachable insert that stays cleaner around the exit side of the channels. The present invention also addresses this need.
The present invention relates to a coating device, such as a rotary atomizer, a bell cup thereof, and a detachable flow control device thereof, and methods thereof. The rotary atomizer has a bell cup, i.e., a rotatable body. The bell cup can have a provision for cleaning the outer surface thereof and/or a provision for enabling access to inside, i.e., a cavity thereof, for easier cleaning and/or to alter the flow pattern.
The rotatable body can have a cavity defining an inner surface, an outer surface surrounding the cavity, and a spray edge located at a distal end of the rotatable body, where coating material to be atomized leaves the rotatably body. The rotatable body further can have a first axial passage through which a coating material to be atomized or a cleaning agent can be delivered to the cavity. The rotatable body has a plurality of cleaning passages extending from the first axial passage to the outer surface of the rotatable body. The cleaning passages are adapted to deliver cleaning agent to the outer surface. Moreover, the outer surface of the rotary body is deliberately devoid of any fluid accumulating recess or reservoir to enable the cleaning passages to feed the cleaning fluid onto the outer surface without accumulating or storing the cleaning agent or the coating material on the outer surface.
The rotatable body can be substantially bell shaped, having an open distal end and a proximal end opposite the distal end, and a hub portion extending axially from the proximal end of the bell shaped body. The outer surface can extend from the hub portion to the distal end. The first axial passage extends concentrically with the hub portion and extends through the proximal end of the bell shaped body to communicate the first axial passage with the cavity. The cleaning passages can extend outwardly and forwardly toward the proximal end of the bell shaped body.
The rotary atomizer can further include a rotatable shaft connected to the rotatable body. In this respect, the hub portion can include a first mechanical connector, such as external or male threads, and the rotatable shaft can include a second mechanical connector, such as internal or female threads, that is complementary to the first mechanical connector.
A stationary nozzle can be used to deliver the coating material and the cleaning agent. In this respect, the nozzle can have a first passage adapted to deliver the coating material to the cavity, at least one second passage adapted to deliver the cleaning agent to the cavity, and a third passage branching off from the second passage. The nozzle can extend into the first axial passage with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle. The distal end of the stationary nozzle can extend into the second axial passage with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle.
The first passage and the second passage both communicate with the cavity, and the third passage communicates with the cleaning passages to direct the cleaning agent to the outer surface. Because the outer surface is devoid of any fluid accumulating recess or reservoir according to the one aspect of the present invention, the cleaning passages can feed the cleaning fluid onto the outer surface without accumulating the cleaning agent or the coating material on the outer surface.
The bell cup can have a flow control device connected or mounted to the rotatable body, which flow control device substantially encloses a portion of the cavity. The flow control device can have a mounting member and a face cover having a front side, a rear side opposite the front side, the rear side facing toward the first axial passage. The mounting member extends from the rear side of the face cover into the first axial passage. The face cover has at least one passageway adjacent its periphery.
The mounting member can include a first mechanical connector and the bell shaped body can include a second mechanical connector that is complementary to the first mechanical connector. The first mechanical connector can comprise external threads and the second mechanical connector can comprise complementary internal threads. The flow control device can be attached or detached by rotating the flow control device relative to the bell shaped body. The internal threads can be formed in the first axial passage.
The face cover can be circular and spaced from a distal end of the first axial passage. The outer periphery of the circular face cover can be spaced from an inner surface to form an annular passageway or can sealingly abut the inner surface to form a plurality of passageways. The rear side and the inner surface define an internal chamber. The mounting member has a second axial passage communicating with the internal chamber and the first axial passage. The second axial passage is adapted to deliver the coating material to the internal chamber.
The flow control device can further include a sealing flange positioned between the first mechanical connector and the face cover. The first axial passage includes, at a distal end thereof, a seat for receiving the sealing flange. The flow control device can further include a plurality of substantially radially extending channels that communicate the second axial passage with the internal chamber. The substantially radially extending channels can be positioned between the sealing flange and the face cover.
The flow control device can further include a recessed cavity formed between the face cover and the sealing flange. The internal chamber is further defined by the recessed cavity. The recessed cavity can have an annular wall positioned between the face cover and the sealing flange. The radially extending channels open through the annular wall and form exit openings that are kept separated by the annular wall. The exit openings each are radiused to form a sharp longitudinal edge formed on the annular wall between two adjacent channels.
The flow control device can further include a center feed outlet at a center of the face cover. The center feed outlet can comprise a center passage communicating the internal chamber with the front side of the face cover and a plurality of substantially radially extending channels communicating with the center passage. The front side can be substantially planar and the substantially radially extending channels can extend substantially parallel to the planar front side.
Another aspect of the invention is a flow control device itself, having aforementioned face cover, mounting member, sealing flange, axial passage, plurality of substantially radially extending channels, and annular wall. Specifically, the face cover has a front side and a rear side opposite the front side. The mounting member extends from the rear side of the face cover and has a mechanical connector adapted for attachment to a complementary mechanical connector of a bell cup of the rotary atomizer. The sealing flange is positioned between the mounting member and the face cover. The axial passage extends through the mounting member and the sealing flange. The substantially radially extending channels communicate with the axial passage and are positioned between the sealing flange and the face cover. The annular wall is formed between the face cover and the sealing flange. The radially extending channels open through the annular wall and form exit openings kept separated by the annular wall. The exit openings each are radiused to form a sharp edge formed on the annular wall between two adjacent channels. The radius reduces the wall surface so that the paint exiting the channels has virtually no surface to accumulate. Thus, cleaning the bell becomes much more efficient.
According to another aspect of the invention, one method of delivering coating material and cleaning agent to a rotary atomizer comprises: providing the rotatable body having the cavity defining the inner surface, the outer surface surrounding the cavity, and the spray edge at the distal end of the rotatable body, where the coating material to be atomized leaves the rotatably body, with the outer surface that is devoid of any fluid accumulating recess or reservoir; providing the stationary nozzle having the first passage that delivers the coating material to the cavity, the second passage that delivers cleaning agent to the cavity, and the third passage branching off from the second passage; providing a first axial passage in the rotatable body and the cleaning passages in the rotatable body, extending from the first axial passage to the outer surface of the rotatable body; extending the stationary nozzle into the first axial passage with a sufficient clearance to permit the rotatable body to freely rotate relative to the stationary nozzle; feeding coating material through the first passage to deliver coating material to the cavity and thus to the spray edge while rotating the rotatable body or feeding cleaning agent to the cavity through the second passage and to the outer surface through the second and third passages and the cleaning passages while rotating the rotatable body.
Because the outer surface is devoid of any fluid accumulating recess or reservoir, the cleaning passages feed the cleaning fluid onto the outer surface without accumulating the cleaning agent or accumulation the coating material on the outer surface.
According to another aspect of the invention, a method of manufacturing a bell cup comprises: providing the bell shaped body having the cavity defining the inner surface, the outer surface surrounding the cavity, and the spray edge at a distal end of the rotatable body, where the coating material to be atomized leaves the rotatably body; providing the first axial passage in the rotatable body that communicates with the cavity; providing the flow control device comprising the face cover and the mounting member, the face cover having the front side, the rear side opposite the front side, the rear side facing toward the first axial passage, and wherein the mounting member extends from the rear side of the face cover into the first axial passage, and the face cover having a plurality of passageways adjacent its periphery; providing the first mechanical connector on the mounting member and the second mechanical connector that is complementary to the first mechanical connector on the first axial passage; and connecting the first and second mechanical connector.
Because the first and second mechanical connectors can be detachably connected, using, for example, threads or any suitable conventional mechanical connectors, the flow control device can be removed to fully expose the cavity and to readily replace the same for different flow control or spray pattern.
The present invention encompasses the above-described aspect or combination of the aspects described above, or other features described below.